Abstract: Once the pipeline joint coating fails, the corrosive medium will seep into the pipeline through the crack, which will seriously impact the integrity of the pipeline. In this paper, the identification and determination process of joint coating failure was put forward based on the principles of magnetic flux leakage in-line inspection(MFL ILI)and the forms of joint coating failure. That is to determine the corresponding relation between the feature of the external corrosion caused by joint coating failure and the feature of MFL ILI signals by analyzing the structural characteristics and failure forms of pipeline joint coating and the position and morphological characteristics of the possible corrosion defects, so as to identify the pipeline joint coating that may have failed. Then, based on actual excavation results of many pipelines, the precision ratio of MFL ILI technology to identify and determine the joint coating failure was calculated, and its correctness was verified. It provides the foundation for the industrial application of the joint coating failure identification and determination technology based on MFL ILI.